Conventionally, relating to a display device, a method of providing a plurality of optical sensors in a display panel so as to provide an input function such as a touch panel, pen inputting, or a scanner, etc. has been known. In order to apply this method to a mobile machine used in various light environments, it is necessary to eliminate influences of light environments. Then, a method for determining a signal to be input by removing a component depending on light environments from a signal detected by an optical sensor has been known as well.
JP4072732B discloses that, in an input/output device in which light-receiving elements are provided so as to correspond to display elements, respectively, the reset and the readout are carried out line-sequentially with respect to the light-receiving elements, by blinking a backlight once during one frame period, so that an amount of light during a backlight ON period, and an amount of light during a backlight OFF period are obtained from all of the light-receiving elements during one frame period.
FIG. 22 shows backlight ON and OFF timings and reset and readout timings with respect to light-receiving elements disclosed in JP4072732B. As shown in FIG. 22, the backlight is on during a former half of one frame period, and is off during a latter half of the same. During the backlight ON period, the reset is carried out line-sequentially with respect to the light-receiving elements (solid line arrows), and the readout is carried out line-sequentially with respect to the light-receiving elements (broken line arrows). During the backlight OFF period as well, the reset and the readout with respect to the light-receiving elements are carried out in the same manner.
JP3521187B shows a solid image pickup device having a unit light-receiving part shown in FIG. 23. The unit light-receiving part shown in FIG. 23 includes one photoelectric conversion portion PD and two charge accumulation portions C1 and C2. When both of reflection light from an object that reflects light from a light emitting means and external light are received, a first sample gate SG1 is turned on, and electric charges generated by the photoelectric conversion portion PD are accumulated in the first charge accumulation portion C1. When only external light is received, a second sample gate SG2 is turned on, and charges generated by the photoelectric conversion portion PD are accumulated in the second electric charge accumulation portion C2. A difference between amounts of charges accumulated in the two charge accumulation portions C1 and C2 is determined, whereby an amount of light reflected by an object that reflects light from a light emitting means can be determined.
Generally, in a display device including a plurality of optical sensors in a display panel, the readout from optical sensors is carried out line-sequentially. A backlight for mobile equipment is turned on at once, and is turned off at once, for the entire screen.
An input/output device disclosed in JP4072732B carries out the reset and the readout during respective non-overlapping periods in a backlight ON period, by blinking a backlight once during one frame period, and carries out the reset and the readout during respective non-overlapping periods in a backlight OFF period as well. Therefore, it is necessary to carry out the readout from light-receiving elements within a ¼ frame period (e.g., within 1/240 second in the case where the frame rate is 60 frames/second). Practically, however, it is considerably difficult to carry out such a high-speed readout.
Further, a period in which light-receiving elements detect light during a backlight ON period (B1 shown in FIG. 22) and a period in which light-receiving elements detect light during a backlight OFF period (B2 shown in FIG. 22) deviate by ½ frame period from each other. Therefore, the followability with respect to motion input fluctuates depending on an input direction. Besides, this input/output device starts readout immediately after the completion of reset, and the reset is started immediately after the completion of readout. Therefore, lengths and intervals of the backlight ON period and the backlight OFF period cannot be determined freely.
Further, this input/output device detects an amount of light during the backlight ON period and an amount of light during the backlight OFF period with the same light-receiving elements. Therefore, when an amount of light during the backlight ON period is detected with a certain light-receiving element, the detection of an amount of light during the backlight OFF period by the light-receiving element concerned cannot be started until the readout of the amount of light that has been detected by the light-receiving element concerned during the backlight ON period is completed.